Support operations

New Support endpoint operations:

• Get a request — Get a single ticket's details.
• List request comments — List a ticket's comments.
• Add a comment — Add comment to a ticket.

New schemas:

• TicketDetailExtAPI — Extend TicketListItem with description.
• CommentExtAPI — Comment with author email and Unix ms timestamp.
• CommentsResponseExtAPI — Comments array (no pagination).
• CreateCommentRequest — Body and optional private flag.